Methods for Measuring and Monitoring Soil Carbon
Sequestration
R. César Izaurralde
PNNL, Joint Global Change Research Institute
www.globalchange.umd.edu
l b l h
d d
US Senate Agriculture Committee Briefing
Washington, DC
March 20, 2009
Measuring and monitoring soil C
sequestration: a new challenge?
Soil scientists have been measuring and
g soil carbon in long-term
g
monitoring
experiments for many decades
Soil survey maps can be used to estimate the spatial
di t ib ti off soil
distribution
il organic
i C stocks
t k
The challenge consists in developing cost-effective
methods for detecting changes in soil organic C that
occur in fields as a result of changes in management
Detecting, measuring and scaling soil
carbon sequestration
ƒ
Detecting changes in soil C stocks
Difficultl iin the
Diffi
h short
h term
Changes to be detected small
compared to total C stocks
ƒ
Methods for detecting and scaling
soil C sequestration
Direct methods
Field and laboratory
measurements
Soil sampling
Wet and dry combustion
Eddy covariance
Indirect methods
Accounting
g
Remote
sensor
Captured C
Woodlot C
Respired C
Databases / GIS
Harvested C
Litter
C
Heavy
fraction
C
Light
fraction
C
Simulation models
Eddy flux
Cropland C
Root C
Respired C
Sample
probe
Eroded C
g
C
Soil organic
SOC t = SOC 0 + C c + C b - C h - C r - C e
Buried C
W etland C
Soil profile
Soil inorganic C
Stratified accounting with databases
Remote sensing
Simulation modeling
Century, DayCent
RothC
EPIC, APEX
DNDC
DSSAT
Post et al. (2001)
Soil sampling protocol used in the Prairie
Soil Carbon Balance (PSCB)
in
(
) project
p j
Canada
Use “microsites” (4 x 7 m) to reduce
spatial variability
Three to six microsites per site
Calculate soil C storage on a soil mass
equivalence basis
Analyze samples at the same time
Detection of soil C changes in 3 years
0.71 Mg C ha-1 – semiarid
1.25 Mg C ha-1 – subhumid
N
5m
initial cores (yr 1997)
initial cores (yr 1997) with
buried marker (electromagnetic)
2m
subsequent cores (yr 2002)
Ellert et al. (2001)
McConkey et al. (2001)
Three emerging technologies to measure
soil C directly in the field
Laser Induced Breakdown Spectroscopy:
LIBS
Based on atomic
emission
i i
spectroscopy
Portable
A laser pulse is focused on a soil
sample, creating high temperatures
and electric fields that break all
chemical bonds and generating a
white hot plasma
white-hot
The spectrum generated contains
atomic emission peaks at
wavelengths characteristic of the
sample’s constituent elements
A calibration curve is required to
predict soil C concentration
Cremers et al. (2001) J. Environ. Qual. 30:2202-2206
Inelastic Neutron Scattering: INS
In situ, non-destructive technique
th t consists
that
i t in
i directing
di ti ffastt
neutrons (14 MeV) produced by a
neutron generator into the soil,
where they interact with the nuclei
of atoms including 12C and other
atoms (H, N, O, Si, K, Ca, P, etc.)
Fast neutrons collide with C, H, and
N atoms and release gamma rays
with
ith energies
i off 4.4,
4 4 2.2,
2 2 and
d 10
10.3
3
MeV
Soil mass interrogated: >200 kg
The INS was tested in stationary
and scanning modes
Wielopolski et al. (2000) IEEE Trans. Nuclear Sci. 47:914-917
Mid-Infrared Reflectance Spectroscopy:
MIRS
Unlike LIBS and INS, MIRS
probes the bond identities of a
sample's molecules, offering the
possibility of directly
distinguishing inorganic from
organic C,
C thus eliminating the
need for acid pretreatment to
remove inorganic C
Yet for the same reason,
quantifying soil C must be done
indirectly, by recourse of
advanced data-fitting routines
that require libraries of soil
spectra vs. soil C data
McCarty et al. (2002) Soil Sci. Soc. Am. J. 66:640-646
Detecting and scaling changes in soil C by
direct methods
methods, simulation modeling
modeling, and
remote sensing interpretation
Base data
Land units
Databases
Sampling design and data
Statistical power
Baselines
Sampling and processing
Depth and depth increments
Bulk density
Ancillary measurements
Crop and biomass yields
Inputs and management
Environmental conditions
Modeling and remote sensing
Models and model complexity
Remote sensing
Crop identification
Crop residue cover
Reporting results
Equivalent soil mass
Izaurralde and Rice
(2006)
COMET - VR: an example of an integrated
soil carbon monitoring
g system
y
Sampling network data
In summary…
Soil carbon changes can be measured with accuracy adequate for
monitoring protocols following accepted methods of soil sampling and
analysis
Several advanced technologies to measure soil carbon directly in the
field appear promising for fast, accurate, and cost-effective monitoring
projects
j t
Integrated modeling-measurement systems can provide reliable, costeffective quantification to support agricultural GHG mitigation policies
Efforts are needed to establish broad-scale
broad scale, regional networks of soil
C monitoring locations (via national/international efforts or ‘data
pooling’ from pilot projects)